As illustrated in FIG. 1, a conventional ultrasound imaging system includes a processing unit 1, a display unit 2, a cable 3 and an ultrasound transducer unit or probe 4. The probe or transducer 4 is connected to the processing unit 1 via the cable 3. The processing unit 1 generally controls the transducer unit 4 for transmitting ultrasound pulses towards a region of interest in a patient and receiving the ultrasound echoes reflected from the patient. The processing unit 1 concurrently receives from the transducer unit 4 in real time the reflected ultrasound signals for further processing so as to display on the display unit 2 an image of the region of the interest.
Diagnostic imaging includes the assessment of blood perfusion for several applications and especially in ultrasound analysis. The perfusion assessment is based on the analysis of a sequence of ultrasound contrast images that are obtained after administering an ultrasound contrast agent (UCA) to a patient. One exemplary UCA is suspensions of gas bubbles in a liquid carrier and is referred to as gas-filled microvesicles. Another kind of UCA is suspensions of porous microparticles of polymers or other solids, which carry gas bubbles entrapped within the pores of the microparticles. In general, the contrast agent acts as an efficient ultrasound reflector of ultrasound waves which result in echo-power signal. Since the contrast agent flows substantially at the same velocity as the blood in the patient, its tracking provides information about the perfusion of the blood in a region of interest.
In a typically implemented destruction-replenishment technique, the organ is perfused with the contrast agent such as microbubbles at a constant rate, and the microbubbles are then destroyed by a flash of sufficient acoustic energy in the imaging plane. Quantitative information about the blood perfusion is derived by measuring echo-power signal over time of the replenishment or reperfusion of the microbubbles in a region of interest (ROI). The above measuring technique requires a constant and continuous supply of the contrast agent, called infusion. The continuous administration requires a specific push-syringe pump introducing an additional level complexity in the medical contrast exam. In addition, increase in cost is possible because more than one vial of contrast agent may be necessary. Finally, potential bio-effects may result from the use of a high acoustic energy level in combination with microbubbles.
Another perfusion technique is a bolus that is a single dose of the contrast agent which is provided over a short period of time, typically in the range of 2 to 20 seconds. In comparison to the destruction-replenishment technique, the bolus technique is simpler to control and is less costly. Following bolus intravenous administration in bolus, the contrast uptake in a given organ increases over time (wash-in phase) to reach a maximum value and then gradually decreases (wash-out phase). In general, since the contrast uptake kinetics is spatially varying in the body, the current mathematical modeling techniques known in the art are not necessarily suitable for a rigorous representation of the perfusion process.
Upon focusing in one particular region of interest (ROI), certain mathematical models may be suitable for a rigorous representation of the perfusion process. On the other hand, the blood flow is all inclusive or non-discriminatory in its direction with respect to the ROI.
For the above reasons, it remains desirable to refine the assessment of the perfusion process for a rigorous representation of the perfusion process in a particular ROI.